1. Field of the Invention
This invention relates to the field of telecommunications. More precisely, the invention proposes a new coding and decoding method for a high-speed data transmission, particularly in a home or office environment.
2. Description of Prior Art
Some constraints have to be respected during the data sending and transmission phase for data transmission applications in interior and exterior environments, particularly limiting the radiation spectrum. These constraints are applicable particularly to transmissions in a home or office environment. Thus, according to electromagnetic compatibility standards in force, the radiation spectrum must respect a jig limiting radiation beyond 30 MHz. Some coding methods are used for data transmission in an intra-building environment, particularly in order to limit radiation beyond 30 MHz, while maintaining a high speed.
Thus a first coding system, MLT3 (MulTiLevel 3) coding system more particularly described in detail in standard IEEE802 3, is used for example in 100BaseT type interfaces. In this coding system, bits equal to “1” correspond to a transition, while bits equal to “0” correspond to a lack of transition. Thus, only bits equal to “1” will cause a change in the state signal. They are coded successively on 3 states, for example such as −V, 0, +V. Bits equal to “0” are coded using the previously transmitted value.
The main advantage of the MLT3 coding system is that it significantly reduces the frequency necessary for a given speed, due to the use of three states. For example, for a speed of about 100 Mbits/s, the maximum parasite frequency of the signal is about 25 MHz.
One major disadvantage of this coding system is due to the long sequences of bits equal to “0” that appear in this code and that can cause a loss or phase shift of the receiver clock. Coded data are scrambled before being transmitted to overcome this problem, which reduces the improvements provided by this code.
Moreover, the Hamming distance between valid code words is very small (equal to one), which facilitates transmission errors that might occur in coding or in scrambling. There is then a risk of accepting invalid code words or rejecting valid code words.
Finally, with this code it is difficult to control the radiation spectrum and it does not have particularly interesting error detection or correction properties.
Other coding methods used to obtain a radiation spectrum partly respecting the limitation of radiation beyond 30 MHz are also envisaged according to prior art.
These coding methods are capable of cancelling the DC component of data to be transmitted on average or for each symbol transmitted.
Cancellation of this DC component (DC balancing for direct component balancing), provides a means of obtaining a radiation spectrum partly respecting a jig imposed by intra-building transmission standards, limiting radiation beyond 30 MHz.
For example, one such method uses the Widmer and Franaszek coding (A. X.
Widmer and P. A Franaszek, IBM Journal of Research and Development, Vol. 27 No. 5, p. 440, September 1983), used in the IEEE 1394b standard. This coding can result in 10-bit words starting from 8 bit words, using a DC balancing technique.
This technique cancels the average DC component, and not the DC component for each transmitted symbol.
However, it has the disadvantage that it enables successive transitions. The result is non-negligible radiation beyond 30 MHz. The spectrum then does not fully respect the jig specified in frequency emission standards. Therefore this code only partly satisfies the specified constraints.